The present invention relates to a labeling area determining apparatus and a magnetic resonance apparatus which determine a labeling area in an ASL (Arterial Spin Labeling) imaging method, and a program therefor.
In a magnetic resonance imaging (MRI) apparatus, a subject to be imaged is carried in an internal bore of a magnet apparatus, i.e., an imaging space with a static magnetic field formed therein. A gradient magnetic field and an RF (Radio Frequency) magnetic field are applied thereto to excite spins in the subject and thereby generate magnetic resonance signals, whereby an image is reconstructed based on the received signals from the magnetic resonance signals.
Using such an MRI apparatus, there has been known perfusion imaging by an imaging method called ASL. In this imaging, magnetic labeling is performed on each spin on the upstream side of a blood flow of an object to be examined or a subject, and magnetic resonance signals produced by the inflow of the labeled spins in a region of interest are used in the imaging. The labeling may also be called tagging, but is referred to as labeling in the present disclosure.
The labeling is performed by inversion of each spin. When the perfusion of a cerebral blood flow is imaged, the spin's inversion is performed on the neck of a subject, so that a perfusion image about a desired slice of a brain is imaged. The perfusion image is determined as an image of a difference between a label image being a tomographic image with labeling and a control image being a tomographic image with labeling (refer to, for example, Japanese Patent No. 4051232).
In the ASL imaging method, an area (plane) to perform labeling may be an area less reduced in branch and flexion. The area to perform labeling should be determined in such a manner that the direction of the normal to the area substantially coincides with a blood flow direction to prevent timings each provided to cause a labeled blood flow to flow into a region of interest from varying for every blood vessel. For this reason, generally, the labeling area is determined in such a manner that the direction of a normal line substantially coincides with a body axial direction of a subject around a lower part of such a circle of Willis (also called an arterial circle of the cerebrum) as shown in FIGS. 13A and 13B.
When, however, the posture of the head of the subject changes, the arteries lying around the lower part of the circle of Willis are moved/transformed and then tilted, so that an area suitable for labeling also changes. Therefore, when the labeling area is determined as usual in such a manner that the direction of the normal thereto coincides with the body axial direction of the subject, there is a case where the labeling area is not appropriately determined depending on the posture of the head.
With such a foregoing in view, there has been a demand for a technology capable of appropriately determining a labeling area of each spin without depending on the posture of a head to be imaged, upon imaging by the ASL method.